1. Field of Invention
This invention relates to a novel plastic syringe. More specifically, this invention relates to a plastic syringe for use with a power injector.
2. Description of the Related Art
The use of contrast media for image enhancement in medical diagnostic imaging is widespread. For example, x-ray contrast agents, which are typically iodinated contrast agents, such as the nonionic contrast agent iohexol, have gained widespread commercial acceptance in various x-ray imaging procedures such as x-ray computed tomography (CT).
To effect introduction of contrast media into body cavities such as the vascular network, it has been common practice to utilize injector syringes in combination with catheters. The syringe can be mounted in a power injector apparatus, with the distal end of the syringe being connected to the catheter which is introduced into the system to be studied. It has been estimated recently that of the approximately 9 million contrast enhanced CT scans performed in the United States each year, about one-half involve power injectors and the number is growing. Additionally, approximately 90% of the 1.3 million cardiac angiographic procedures which take place annually in the United States involve power injectors.
The use of prefilled syringes, i.e., syringes prefilled with a unit dose, e.g., of contrast media, with such power injectors provides greater convenience and safety to the health care worker while minimizing waste. For example, the need to transfer contrast media from glass containers to empty syringes can be entirely eliminated. Additionally, risks of contamination associated with preparing sterile contrast agent for injection into the patient can be reduced.
Power injectors for various CT procedures such as angiography are described, e.g., in U.S. Pat. No. 4,006,736; U.S. Pat. No. 4,677,980; U.S. Pat. No. 4,854,324; U.S. Pat. No. 4,911,695; and U.S. Pat. No. 5,007,904. The power injectors described in these patents are of the rear-loading type, i.e., syringes are rear-loaded into a pressure jacket of the injector. More specifically, these injectors comprise a rotatable turret which carries a pair of the pressure jackets and which is rotatable so that when one of the pressure jackets into which a syringe has been rear-loaded is in an injection position, the other pressure jacket is in a position in which a syringe can be rear-loaded. Subsequently, when injection of liquid from the first syringe is completed, the turret is rotated to move the first syringe to an unloading position. When the pressure jacket and its associated syringe has been located in the injection position, a drive member of the injector is moved forward to become drivingly engaged with a plunger in the syringe.
European Patent Application No. 584,531 describes a front-loading medical injector wherein a syringe is mountable upon and removable from a front wall of an injector housing or mounting plate. The front-loading injector includes a readily releasable mechanism for supporting the syringe on the front wall of an injector housing for an injection operation. The releasable mechanism includes at least one retaining portion on the mounting mechanism releasably engageable with a mating retaining portion on the syringe. In addition to enhanced setup convenience, such a front-loading injector provides additional advantages to the health care worker. By not being enclosed in a pressure jacket, the health care worker is better able to view the status of the syringe visually during an injection operation. By allowing the health care worker to better see the syringe, the worker can readily determine whether the syringe is empty or full, the amount of contrast medium delivered, the presence or absence of bubbles, etc.
Heretofore, plastic syringes have been provided for such front-loading power injectors. One such syringe comprises a set of radially extending lugs spaced 180 degrees apart which engage two mating slots in a mounting plate on the power injector by inserting the syringe lugs into the slots and rotating the syringe 90 degrees. This design has achieved some success with a syringe fabricated of polyethylene terephthalate (PET). However, this and other designs proposed in European Patent Application No. 584,531 are less than adequate for some plastics, particularly those of low modulus and/or yield strength, due to the fact that stresses generated during injection can cause localized and/or complete shearing of the lug off the barrel.
Furthermore, PET, when autoclaved at 210.degree. F., undergoes a phase transition from a clear amorphous state to an opaque crystalline state. This is undesirable because one of the dangers associated with the injection of fluids into a patient is a the risk that air will be accidentally injected into the patient. The presence of a transparent syringe barrel enables the health care worker to readily detect empty and/or partially filled syringes prior to an attempted injection. Thus, it would be highly desirable to be able to replace PET in a plastic syringe for use with power injectors with other plastic materials which can be autoclaved without compromising clarity.